| Message ID | 20240902130329.3787024-4-yukuai1@huaweicloud.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | block, bfq: fix corner cases related to bfqq merging | expand |
On Mon 02-09-24 21:03:28, Yu Kuai wrote: > From: Yu Kuai <yukuai3@huawei.com> > > Consider the following scenario: > > Process 1 Process 2 Process 3 Process 4 > (BIC1) (BIC2) (BIC3) (BIC4) > Λ | | | > \-------------\ \-------------\ \--------------\| > V V V > bfqq1--------->bfqq2---------->bfqq3----------->bfqq4 > ref 0 1 2 4 > > If Process 1 issue a new IO and bfqq2 is found, and then bfq_init_rq() > decide to spilt bfqq2 by bfq_split_bfqq(). Howerver, procress reference > of bfqq2 is 1 and bfq_split_bfqq() just clear the coop flag, which will > break the merge chain. > > Expected result: caller will allocate a new bfqq for BIC1 > > Process 1 Process 2 Process 3 Process 4 > (BIC1) (BIC2) (BIC3) (BIC4) > | | | > \-------------\ \--------------\| > V V > bfqq1--------->bfqq2---------->bfqq3----------->bfqq4 > ref 0 0 1 3 > > Since the condition is only used for the last bfqq4 when the previous > bfqq2 and bfqq3 are already splited. Fix the problem by checking if > bfqq is the last one in the merge chain as well. > > Fixes: 36eca8948323 ("block, bfq: add Early Queue Merge (EQM)") > Signed-off-by: Yu Kuai <yukuai3@huawei.com> Looks good. Feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > block/bfq-iosched.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c > index ffaa0d56328a..ca766b7d5560 100644 > --- a/block/bfq-iosched.c > +++ b/block/bfq-iosched.c > @@ -6727,7 +6727,7 @@ bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq) > { > bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue"); > > - if (bfqq_process_refs(bfqq) == 1) { > + if (bfqq_process_refs(bfqq) == 1 && !bfqq->new_bfqq) { > bfqq->pid = current->pid; > bfq_clear_bfqq_coop(bfqq); > bfq_clear_bfqq_split_coop(bfqq); > -- > 2.39.2 >
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index ffaa0d56328a..ca766b7d5560 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -6727,7 +6727,7 @@ bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq) { bfq_log_bfqq(bfqq->bfqd, bfqq, "splitting queue"); - if (bfqq_process_refs(bfqq) == 1) { + if (bfqq_process_refs(bfqq) == 1 && !bfqq->new_bfqq) { bfqq->pid = current->pid; bfq_clear_bfqq_coop(bfqq); bfq_clear_bfqq_split_coop(bfqq);